1. Field of the Invention
The present disclosure relates to a communication system, and more particularly, to an equalization device of a communication system.
2. Description of the Prior Art
In communication systems, inter-symbol interference (ISI) is a common phenomenon. The primary cause of ISI is multipath propagation. When a transmission end transmits a symbol D(0), the symbol D(0) may pass through different paths before arriving at a receiving end. Since the symbol D(0) passing through the different paths corresponds to different delay times, the received signal of the symbol D(0) at the receiving end may include energies of a primary signal R(M1) and at least one interference signal R(M1+N1). Hence, when the transmission end sequentially transmits a plurality of symbols { . . . , D(−3), D(−2), D(−1), D(0), D(1), D(2), D(3), . . . } to the receiving end, the symbols D(N1) sent at time N1 may be affected by the interference signal R(M1+N1) resulting from the previously transmitted symbol D(0).
Equalizers are used to reduce the inter symbol interference (ISI), wherein common equalizers include linear feed-forward equalizers (LE), decision-feedback equalizers (DFE), and Viterbi equalizers. The disadvantage of the linear feed-forward equalizer is that noise is increased. A characteristic of the decision feedback equalizer is that ISI can be eliminated without increasing the noise; however, the signal energy cannot be fully utilized. A characteristic of the Viterbi equalizer is that the signal energy of the ISI can be fully utilized rather than be eliminated. When the length of multipath channel which produces the ISI (marked as “L”) gets larger, however, the complexity of the Viterbi equalizer is directly proportional to “2^L”. In other words, the complexity of the Viterbi equalizer is greatly increased as “L” is increased.
Hence, how to fully utilize the energies of the received signal while reducing the amount of operations of the Viterbi equalizer has become an important topic in this field.